Electrically initiated spotter tracer bullet



A g- 20, 19 3 T. STEVENSON ETAL 3,101,054

ELECTRICALLY INITIATED SPOTTER TRACER BULLET Filed Oct. 5, 1960 INVENTORS THOMAS STEVENSON WINSTON W. CAVELL WILLIAM A. DISCHERT A W W ATTORNEY United States Patent r 3,101,054 ELEC'I'RICALLY INITIATED SPOTTER TRACER BULLET Thomas Stevenson, Huntingdon Valley, and Winston W. Cavell, Philadelphia, Pa., and William A. Disehert, MerchantvilleyNd assignors to the United States of America as represented by the Secretary of the Army Filed Oct. 5, 1969, filer. No. 60,758

7 Claims. (Cl. 102-60) (Granted under Title35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes withoutthe payment to us of any royalty thereon.

= This invention relates to a small arms projectile and has for its object to provide a means of developing an electrical charge in the bullet for igniting a spotting type explosive on contact or on reduction of its velocity without stoppage of the projectile. In spotting rifles, i.e., those aflixed to a large caliber weapon usually of a recoilless type, there has long existed a need for ignition of the pyrotechnic spotting explosive on impingement of the projectile or a light graze impact on hard surfaces or soft mud in order that the gunner may be advised where the first hit occurs even though the projectile may not be stopped. Heretofore the spotting type explosives in such small armsprojectiles have been of the'type requiring a considerable impact force upon a somewhat unyielding surface.

According to this invention that old need has now been filled by providing a system within the projectile which will generate and hold suflicient electrical energy to fire the primer without the need to crush the projectile nose or have it sustain relatively heavy impact thus obtaining a higher reliability of function. The spotting explosive being fired in response to only a slight reduction in veloc ity of the projectile. More specifically a tracer composition in the rear of a projectile is ignited by the propellantblast on firing the spotting rifle.

Around the tracer composition and close thereto for reception of heat and pressure from the tracer composition is a barium piez-o electric crystal capable of generating a substantial voltage for charging an electric condenser before the crystal undergoes transition from the polarized to the unpolarized state by theaction of pressure, crushing, or by heating the crystal to 120 C., its'ourie temperature. To prevent the charge generated from flowing back to the crystal a way of allowing ourrent to flow inonly one direction is provided such as a rectifier or a spark gap.

The'latter is preferred-because of itssimplicity and compactness. After thecrystal reachesits curie temperature the-condenser remains char-ged'until velocity of the projectile is reduced suddenly even though only slightly and a switch is closed to supply current from the condenser to the electrically initiated primer and spotting type pyrotechnic explosive. To'efi'ect closure of such a switch the condenser is made bodily slidable to move one switch This projectile is providedwith usual jacket 10 of gliding metal or the likelextending from itsnose 11 to w I its rear end portion leaving an opening 12 into which a propellant flame may extend initially on firing to ignite a usual tracer composition 13. A closure cup 14 oi easily burstable or consumable material normally keeps out Patented Aug. 20, 1963 moisture from the tracer composition 13 and its customary igniter or primer 15. The container 16 for the tracer is thin walled at its forward portion 17 to facilitate the conduction of heat and pressure from the burning tracer to the inner surface of a barium titanate piezoelectric crystal 18 in cylindrical shape, a thin brass sleeve 19 surrounds the outside of the crystal to conduct current generated by heat and by pressure on the crystal to an electric condenser 20 via a spark gap 21 of .003 of an inch in size in a plastic insulating washer 22 of this thickness. During charging the circuit from the crystal is through brass plate 19a, the spark jumps the air gap 21 to the rear metal condenser lead 23 to the condenser20, through the frontcon'denser lead 24 thence through front contact ring 29 to the jacket 10 and back to the crystal through the container 16 and 17 After being charged to its maximum voltage the condenser undoubtedly loses some of its peak voltage back'through the crystal until The crystal 18 generates current due to both heat and pressure sufficient to generate a current of at: least a thousand volts or more beginning during the travel of the projectile in the gun according toestimate and breaking down the air gap 21. The crystal becomes inactive at a temperature of about (3., its curie temperature.

For discharge of the condenser, the circuit as shown in FIG. 2 is through the .front condenser lead 24 and its forward projection contact 25a to primer button 25, primer mixture 27 primer cup 26 jacket 10, rear contact ring 28 to condenser 20. During discharge the forward contact ring 29 is not in contact with the forward condenser-lead 24 as it was during charging; r V

The sensitivity of the projectile to a sudden reduction in its velocity depends to a large extent upon the strength of creep spring 30. A light spring ofiers little resistance to a sudden reduction in velocity of only a small amount. Of course the condenser need only make contact and slide forward bodily with ease to discharge into the primer 27. The mass of the condenser should besmall enough so that a normal and gradual reduction in speed ofthe projectile will notcause it to slideforward and ignite the primer mixture 27 prematurely. The primer support metal cup 32 has a central opening closed. hythe consumable foil paper closing that opening and keeps the primer composition separate from the, spotter composition 31 yet enables the primer flame to quickly penetrate and ignite the spotter mixture. The creep spring housing 33 and the primer insulation 34lai'e plastic material of which several types could be used successfully. The heavy lead slug 35 gives the .50 caliber spotting projectile greater momentum in order that its trajectory will more closely approach that of the projectile fired by the large caliberjgun as is'known in the'art to be desirable. It is believed thatthe temperature and'pressure of the burriing propellant alone aIl'dWWlthOli't any tracer composition being present should be enough to adequately charge the condenser during travel of the projectile within the gun, the tracer composition being left outrbut the tracer gives added reliability. The normally slightly oversize projectiles should cause enough heat to be generated by the engravingoperation of the riding and-friction to charge the condenser. Inrfactany sohrce of heat or pressure would sufli'ce toetfectivelylenergize the piezo crystalnforr charging of the condenser. .A noteworthy feature of the embodiment illustrated is the: tact that an delay there may be in getting the heat and pressure, either or both of them to be'transferred'through the thin Wall portion 17 of the tracer'container lti. Instead of a tracer mixturebeing ignited,- a small charge of incendiary or a high explosive is also capable of activating the system.

A piezo electric crystal of flat and of shapes other than cylindrical may be used; So also. more than one crystal may be desirable. V

we claim:

1. In a spotting projectile having a body, an explosive therein in 'a forward portion of said projectile, and means for igniting said explosive, the combination therewith of the improvement in said igniting means whereby it maybe responsive to a reduction in the velocity of the projectile of the type experienced in a graze impact, said improvement including apiezoelectric crystal responsivev to heat and pressure applied to a surface of the crystal from a spotting rifle, an electrical condenser within 'said projectile behind said explosive, circuit means for chargforwardly of said condenser and alsofixed with respect to the, projectile body, a spring engaging said weight and second abutment and of a strength :tobe substantially compressed by a reduction in velocity of the projectile before reaching a target and n excess of that to which the'projectile'is subjected in its free travel in its trajectory'due to air resistance and Weather conditions, a condenser discharge circuit'for firing said explosive, said secondabntment forming a portion of said condenser dischargejcircuit in response to a forward sliding vmovement of said weight and compressicnof said spring to ap-redetermined amount for closing said discharge circuit. a V

2. A-cornbination according to claiml in which said 7 condenser and'saidfslidable weight are a functionally integral unit and said means for. charging saidcondenser from said crystal includes a circuit having therein a spark gap 70f a size capable of'bcin'g bridged by current from said crystal. in advance of the crystal being heated to its" .curie temperature whereby thereafter there is no danger of the-condenser losing its change through said crystal and charging-circuit.

3 Aiconrbination according'to claim 2'in which said condenser discharge circuit includes a primer mixture adjacent said explosiveQand av contact element carried g by said .slidable condenser weight for closingzsa'id discharge circuit through said primer mixture on compres sioniof. said spring -due-to-a graze impact. I

' ,4. --In.a spottingrifleprojectile having a spotting explorsivecompositionin a forward portion thereof, and means [for igniting, said, explosive composition, 'the combination therewith of the improvement in said igniting means for making it i'esponsive to' reduction in velocity'of the projectile due to alightgraze impact on hard surfaces or v oil-soft mud, said improvement including a piezo-electric "crystaI-responsive'to heat and pressure applied ,;to a surdace of the Ecrystalfrom. said rifle, an" electriccondenser,

for charging'said condenser, a spark gapfor opening said ing increase .in velocity, another abutment forward of said condenser fixedto said projectile for holding said c onde'nsje'rgduring reduction in" velocity of said projec-a s tile,,a light spring' between. said condenser and second j mentioned abutmenh a' primer charge for ignitinghsaid" spotting explosive, "and another electrical circuit for firing said spotting explosive and primer charge in response to forward bodily movement of said conden sercompressing said spring and closing said circuit for firing said primer and spotting explosive.

5. A projectile having a rear end permeable to pressure. and heat of propellant gases within a gun from which 7 the projectile is fired, said projectile containing an explosive in a forward portion thereof, a piezoelectric crystal located in rear of said explosive and'in -a rear portionof said projectile to receive heat and pressure from propel 1 lant gases during movement ofjthe projectile. within a gun on firing for generating an electric current, means for securing said crystal adjacent the rear. end of said projectile against coming .out of said 'projectile on set back, :and means for etfecting a delayed firing of said v forwardly located explosive by electrical energy devel oped by said crystal well after said projectile has left a gun from which it is fired, said delayed action means for firing said explosive including heat; and pressure from propellant gases on said crystal from a gun firin-g said projectile, an electric condenser, a circuit between said crystal and condenser, a small air gap in said circuit of a size to break down under voltage developed by said crystal and charge said condenser until said crystal reaches its curie point'after which said gap precludes discharge of the condenser through an impaired'crystal whichhas reached its curie temperature 6. A small arms projectile containing a tracer composition, a piezoelectric crystal around said composition and close enough ttheretotoapply heat and pressure to a surface of said crystal developing duringignition-of said tracer composition, an electric condenser in'frorit of said crystal and longitudinally slidable within said projectile,

an explosive in front of said condenser, circuit connect-ions for charging said condenser'front said crystal, an r air gap of the order of 0.003 inch 'in-saidjcondenser charging circuit, electric connections from" said condenser for V firing said explosive, and a switch in the explosive firing circuit, said switch being closed on movement of said condenseron a reduction in velocity of said projectile."

7. A projectile-having a piezoelectric crystal in the. a r g rear portion thereof; a rear wallhof; said projectile being permeable to heat and pressure from 'a propelling charge, said piezoelectric crystal surrounding an opening into which such heat and pressure mayv enter, means for se-- curing said crystal adjacent said rear wall, ,an ele-ctric condenser charged by said. crystal, -el ect1ical connections between said crystal and condenser, a spotter composition in front-of said condenserg rneans for firing said spotter; composition on discharge of said condenser; saidmeans.

including, a switch wherein one contact thereof is closed. on reduction in velocity of said projectile, andineans in, I

' the connections between thef crystalf and condenser to electricalconnections'hetween said crystal and condenser allow current to flow for'chargingthe condenserandjfor, precluding the condenser being discharged through the T crystalin responseto a forward 'movement-of'- the condenser bodily. l f 1 I n e-rats Cited as iile ofithispa'tent" .7 UNITED. STATES PATENTS, 

7. A PROJECTILE HAVING A PIEZOELECTRIC CRYSTAL IN THE REAR PORTION THEREOF, A REAR WALL OF SAID PROJECTILE BEING PERMEABLE TO HEAT AND PRESSURE FROM A PROPELLING CHARGE, SAID PIEZOELECTRIC CRYSTAL SURROUNDING AN OPENING INTO WHICH SUCH HEAT AND PRESSURE MAY ENTER, MEANS FOR SECURING SAID CRYSTAL ADJACENT SAID REAR WALL, AN ELECTRIC CONDENSER CHARGED BY SAID CRYSTAL, ELECTRICAL CONNECTIONS BETWEEN SAID CRYSTAL AND CONDENSER, A SPOTTER COMPOSITION IN FRONT OF SAID CONDENSER, MEANS FOR FIRING SAID SPOTTER COMPOSITION ON DISCHARGE OF SAID CONDENSER, SAID MEANS INCLUDING A SWITCH WHEREIN ONE CONTACT THEREOF IS CLOSED ON REDUCTION IN VELOCITY OF SAID PROJECTILE, AND MEANS IN THE CONNECTIONS BETWEEN THE CRYSTAL AND CONDENSER TO ALLOW CURRENT TO FLOW FOR CHARGING THE CONDENSER AND FOR PRECLUDING THE CONDENSER BEING DISCHARGED THROUGH THE CRYSTAL IN RESPONSE TO A FORWARD MOVEMENT OF THE CONDENSER BODILY. 